1. Field of the Invention
The invention relates to a memory element and method for forming the same, and more particularly to a phase change memory element memory element and method for forming the same.
2. Description of the Related Art
Electronic devices use different types of memories, such as DRAM, SRAM and flash memory or a combination based on application requirements, operating speed, memory size and cost considerations of the devices. Current new developments in the memory technology field include FeRAM, MRAM and phase change memory. Among these alternative memories, phase change memory is most likely to be mass-produced in the near future.
Currently, a phase change memory cell is developed with several goals in mind: low programming current, higher reliability (including electromigration risk), and smaller cell size. To reduce the programming current, the most straightforward way is to shrink the heating area. A benefit of this strategy is simultaneous reduction of cell size. Yet, as CMOS elements become smaller, forming small contacts to the phase change layer pattern has generally become increasingly difficult. This difficulty arises because the reduction of design rules limit photolithography processes for defining contact images on photoresist layers. Furthermore, limitations to the photolithography process may decrease the flexibility of the phase change memory cell fabrication processes.
U.S. Pat. No. 7,119,353 discloses a phase change memory element 10, referring to FIG. 1, including a substrate 14, a CMOS 12 formed on the substrate 14, a dielectric layer 16, a metal plug 18, and a phase change memory cell 20. Particularly, the phase change memory cell 20 includes a phase change material layer 22, and a pair of electrodes 24 and 26. The CMOS 12 electrically contacts to the electrode 24 of the phase change memory cell 20 via the metal plug 18. Accordingly, the dimension of active area (phase change area) can be determined by the thickness of the phase change material layer 22. As shown in FIG. 1, the contact surface between the phase change material layer 22 and the metal plug 18, however, is limited by the diameter of the metal plug 18, thereby making it unable to increase the heating efficiency and reducing the programming current of the phase change memory cells.
Therefore, it is necessary to develop a phase change memory which mitigates the previously described problems.